The present invention concerns a watch having a case that contains an electronic watch movement and an electric battery assembly including at least one battery or at least one accumulator, the case having a circular bottom opening which allows the battery to be inserted and removed and which is closed in a water-resistant manner by a removable cover provided with bayonet fitting means, the cover including a plate, which covers a housing for the battery and forms at least one part of the back cover of the case, and a substantially annular cylindrical portion, which extends perpendicularly to said case and fits into said opening, said annular portion carrying at least two locking members forming part of the bayonet fitting means.
The removable cover that closes the hatch giving access to the battery assembly can either itself constitute the back cover of the watchcase, or close the opening arranged in a back cover that is itself fixed to the middle part of the case or made in a single piece with said middle part.
The expression “electric battery assembly” here means a source of electric energy, which can include one or more single use batteries, or one or more rechargeable accumulators.
The invention applies particularly, but not exclusively, to electronic watches including one or more additional devices, which consume electric energy, such as for example a device for communication via radio, optical or acoustic transmission, a measuring device using a pressure or other type of sensor, a navigation device, an electronic camera, an electronic diary, etc. In many cases, the energy consumption of these additional devices requires the inclusion in the watch of quite a large electric battery assembly, including either several batteries or accumulators, or a large sized battery assembly or accumulator. The opening necessary in the back cover of the case to give access to the battery assembly can then become very large and extend over most, or all of the surface of the back cover. When the removable cover closing this opening is fixed by a bayonet fitting, the space requirement of the elements of this system and the associated sealing members can cause problems.
EP Patent Application No. 272 515 discloses a wristwatch of the type indicated in the preamble hereinbefore and having a large cover at the back for giving access to the electric battery assembly. In order to allow a reduction in the thickness of the watch, the circular opening of the back cover of the case has a substantially larger diameter than the diameter of the circle circumscribed about the assembly formed by the watch movement and the battery assembly. The bayonet fitting means are arranged outside this circle, at a level located above the bottom face of the movement. The cylindrical annular part of the cover is used to reinforce the latter and to carry at its top the locking members of the bayonet fitting device, which are directed towards the exterior in order to be able to be hooked onto the inner edges of the middle part of the case. Water-resistance around the opening is achieved in a conventional manner, by means of an O-ring joint arranged in a groove of the bottom face of the middle part and compressed axially by the cover.
When the electric battery assembly of the watch has to have a relatively large size in a plane, this design has the drawback of requiring a much larger opening, in order to allow the locking members of the cover to pass between the periphery of the opening and the circle circumscribed about the battery assembly. Moreover, given that the sealing gasket has to have a larger diameter than the opening, the external diameter of the cover is further increased. The large size of the battery assembly thus leads to a very wide watchcase. Another drawback is that if the user has not rotated the cover right in to secure it, water-resistance is not guaranteed since the axial compression of the sealing gasket is likely to be insufficient. The cover has to compress the sealing gasket quite strongly, which involves significant stress on the bayonet fitting locking members.